What problem does it solve? Codebases accumulate shallow modules whose interfaces are nearly as complex as their implementations, making code hard to test, navigate, and change. This Skill provides a shared vocabulary and decision framework for designing deep modules so interfaces stay small while behaviour concentrates behind clean seams. ## Core Features & Use Cases - Deep-module vocabulary: Precise definitions of module, interface, depth, seam, adapter, leverage, and locality, with rejected framings explicitly called out so teams use consistent language. - Dependency-aware deepening: Classifies dependencies as in-process, local-substitutable, remote-but-owned, or true external, and prescribes ports-and-adapters or mock strategies per category. - Parallel interface exploration: A Design-It-Twice workflow that spawns multiple sub-agents to propose radically different interfaces, then compares them on depth, locality, and seam placement. - Use Case: When refactoring a cluster of shallow service classes, use this Skill to decide where the seam belongs, define a port with production and in-memory test adapters, and rewrite tests against the new interface. ## Quick Start Ask the assistant to review a module's interface using the codebase-design vocabulary and suggest how to deepen it.
